<new> Header cannot be found in rtsan

[Sharjeel-Khan]

Our Android LLVM ToT buildbot started failing where it cannot find header anymore when building rtsan. I think it is a libcxx issue over being a compiler-rt/rtsan issue.

FAILED: compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o 
/b/f/w/src/git/out/stage1/./bin/clang++ --target=x86_64-unknown-linux-gnu --sysroot=/b/f/w/src/git/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/sysroot -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/b/f/w/src/git/out/llvm-project/compiler-rt/lib/rtsan/.. -march=x86-64-v2 -D_LIBCPP_AVAILABILITY_HAS_NO_VERBOSE_ABORT=1 -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wno-unused-parameter -O3 -DNDEBUG -fPIC -fPIC -fno-builtin -fno-exceptions -fomit-frame-pointer -funwind-tables -fno-stack-protector -fno-sanitize=safe-stack -fvisibility=hidden -fno-lto -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta -O3 -gline-tables-only -Wno-gnu -Wno-variadic-macros -Wno-c99-extensions -ftrivial-auto-var-init=pattern -DSANITIZER_COMMON_NO_REDEFINE_BUILTINS -fno-rtti -std=c++17 -MD -MT compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o -MF compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o.d -o compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o -c /b/f/w/src/git/out/llvm-project/compiler-rt/lib/rtsan/rtsan_context.cpp
/[b/f/w/src/git/out/llvm-project/compiler-rt/lib/rtsan/rtsan_context.cpp:16](https://cs.corp.google.com/piper///depot/google3/b/f/w/src/git/out/llvm-project/compiler-rt/lib/rtsan/rtsan_context.cpp?l=16):10: fatal error: 'new' file not found
   16 | #include <new>
      |          ^~~~~
1 error generated.

[Sharjeel-Khan]

It was able to bisect it to this commit: b010b7e.

Hey @Meinersbur, do you know why your LLVM_ENABLE_LIBCXX change would cause headers not to be found?

[Sharjeel-Khan]

It got fixed after #153898 reverted #139712.